1. Field of the Invention
The present invention relates in general to a method and variations thereof for making an article, such as cloth, water repellent and/or water resistant. In particular, the method involves the process of providing a thin-layer polymer coating on the article thereby rendering the article water repellent and/or water resistant. Articles made according to the method of the present invention are also disclosed and claimed herein.
2. Brief Description of the Related Art
The formation of thin films on solid surfaces has been the subject of many studies by persons of ordinary skill in the art because of the wide variety of differing films and their individual and unique applications. The preparation of very thin polymer films in adsorbed surfactant bilayers has also been under study, but the results of such studies have oftentimes been inconclusive or unsatisfactory.
Thin film polymerization is carried out in a multi-step process based on the formation of micelle-like aggregates of physically adsorbed surfactants at a solid-solution interface. Such surface aggregates are termed admicelles or hemimicelles. Polymerization of monomers adsolubilized in the admicelles leads to the formation of a thin film on the solid substrate. This technique, which is called admicellar polymerization, is quite versatile and is applicable to a variety of surfaces. Various potential applications have been proposed for thin films formed by this technique such as in the microelectronic industry, particularly for the manufacture of miniaturized circuit patterns on silicon wafers. Other uses include solid lubrication, corrosion inhibition, optical coatings, and surface-modified electrodes.
The present invention is generally directed to a method for producing a hydrophobic cotton fabric wherein this hydrophobic cotton fabric involves a surface coated with a very thin film of polystyrene using an unique admicellar polymerization methodology. By using this method, the hydrophobic cotton fabric retains air permeability thereby allowing for production of a fabric that can be used to produce water repellent garments which are also comfortable to wear and easy to maintain/clean. The present invention, as disclosed and claimed herein, is the first time in the art that admicellar polymerization has been carried out on a textile fabric. Indeed, one of ordinary skill in the art would not have contemplated using such a methodology on a textile fabric because of the inherent misconception of those in the art as to the process of admicellar polymerization. A brief description of the processes and their consequential limitation as known in the art follows hereinafter.
Production of water-repellent textiles has developed from a traditional art to a highly specialized branch of technology during the past century. In the case of cotton, which is a hydrophobic fiber, water repellency is generally imparted by treating the surface of the fabric with a hydrophobic material. Examples of hydrophobic used include materials which have been wax, silicone, and fluorochemicals. Such a treatment usually involves the pad-and-dry process. To improve the breathability of the fabric, Formasa Taffeta Co. Ltd. in Taiwan developed a process employing a porous polyurethane coating to allow air and moisture to pass through the coated fabric. This water-repellent cotton had good air permeability due to the coating of a porous resin on the fabric with specially designed, tightly woven, cloth construction. However, this process resulted in a fabric which was much thicker and heavier than the original fabric. The present invention offers a new method for coating a thin film on a substrate such as cotton which provides a water repellant and/or water resistant fabric that is easily handled and has superior air permeability without creating a thicker than original textile.
The effects of counterion on surfactant adsorption are known in the art. It has been shown that the counterion giving the highest adsorption of surfactant, at a given surfactant and added electrolyte concentration, depends on both pH and fractional surface coverage. The results have suggested that any Region II/Region III transition in the adsorption of surfactant does not occur near the completion of the monolayer coverage nor as a result of electrostatic repulsion of surfactant ions from the mineral surface due to reversal of the net surface charge.
Wu et al. coated polystyrene on alumina surface by using sodium dodecyl sulfate (SDS) as the surfactant in a water/ethanol solution. The treated alumina was analyzed in two parts. The first part was analyzed by FTIR (KBr pellets) and the other one was extracted by tetrahydrofuran (THF) and analyzed by UV spectrophotometer. The results confirmed that admicellar polymerization occurred. Wu et al. found that the polymerization of styrene in the admicelle followed the case IB model in the Smith-Ewart theory. After that, Wu et al. characterized the alumina surface coated with polystyrene. Film thickness ranged from 1.8 to 0.4 nm while BET surface area decreased from 94.7 to 57.8 m2/g. The alumina surface changed from hydrophilic to hydrophobic while retaining the basic pore structure.
Esumi et al. studied polymerization on alumina powder by using sodium 10-undecenoate, which is a polymerizable surfactant. Esumi et al. formed a bilayer of surfactant and polymerized this layer through UV radiation. The dispersion of the alumina particles was studied by looking at mean particle size. Because hydrophilic groups of the surfactant in the second layer were in contact with the aqueous solution, the alumina particles were dispersed due to electrostatic repulsion. The results also showed that purging with nitrogen gas enhanced polymerization.
The incorporation of alcohols into admicelles is also known in the art. It has been found that the surfactant adsorption over most of the isotherm is enhanced dramatically by the presence of alcohol. As the chain length of alcohol is increased, the surfactant adsorption at regions of lower surfactant adsorption was enhanced. A two-site adsolubilization model has been proposed to interpret this complicated system. One of the alcohol sites was the same as in micelles, at the region between the headgroups of the surfactant. The other was a site not present in micelles, the hydrophobic perimeter arising from patchwise adsorption of the disk-shaped admicelle. This model was used to explain: (i) very high ratios of alcohol to surfactant adsorption at lower coverage, (ii) increase of surfactant adsorption below the CMC, and (iii) a slight decrease of plateau adsorption.
Coated polystyrene on precipitated silica is also known in the art. Several types of surfactants consisting of cationic surfactant (CTAB), nonionic surfactant (MACOL), and water-insoluble surfactant (ADOGEN) have been used. Two kinds of polymerization were tested: First, thermal polymerization, and secondly, REDOX polymerization. Due to the effect of head group packing density and length of alkyl chain, the results showed that CTAB adsorbed less than SDS and ADOGEN but greater than MACOL on this substrate. When using AIBN as an initiator, the ratio of initiator to monomer was necessarily high. It has been proposed that the ethanol used to dissolve AIBN consumed many of the radicals formed. For the REDOX system, as the ratio was lower, the reaction took longer to complete. The reduction in the molecular weight of the extractable polymer, as well as the increase in dispersity, was expected. As the chain length of the polymer increases it become more entangled in the surface and more difficult to extract.
Formation of polytetrafluoroethylene (PTFE) on aluminum oxide by admicellar polymerization is also known in the art. In these experiments, ammonium persulfate was used as the initiator. Sodium bisulfate (NaHSO4) and ferrous sulfate (FeSO4) were used as initiator regulators thereby improving the initiator effectiveness at low temperature. The results showed that pressure was the main factor in the control of adsolubilization of the gaseous monomer tetrafluoroethylene into surfactant bilayers. The concentration of the initiator also affected polymerization indicating the analysis of kinetic data must take into account such as the concentration of the initiator. Polytetrafluoroethylene was successfully coated on both aluminum oxide powder and chips. Frictional behavior seemed to be related with film thickness and continuity.
The formation of thin polystyrene films on glass fiber surface has been attempted is known in the art as well. These experiments used the cationic surfactants dodecyl trimethylammonium bromide (DTAB) and cetylpyridinium chloride (CPC). The concentration of styrene used and testing method of treated fiber were tested the same as in the work of Wu et al., except that treated fiber was examined by SEM. The results showed that polystyrene can be coated on glass fiber surface but the SEM micrographs revealed a nonuniform coating on the surface. These experiments showed that polymerization was not restricted to the admicelles and that some polymerization occurred in the supernatant.